1. Field of the Invention
This invention relates to a method for preparing a golf ball mold having improved molding precision and durability at a reduced cost; a golf ball mold which has been prepared by the method; and golf balls molded using the mold.
2. Prior Art
Molds designed to mold golf balls are well known in the art. Most commonly used are golf ball molds of the split type wherein a spherical cavity is internally defined by their internal wall surface having a plurality of projections for forming dimples on a golf ball (referred to as dimple-forming projections). The mold is divided into two mold halves along a parting plane substantially coplanar with the equator of the cavity.
Traditional methods for preparing golf ball molds include hobbing, precision casting, electric discharge machining, and electroforming. In the hobbing technique, a thin sheet metal is interposed between a hemispherical master male die or hob (or base pattern) having a plurality of dimples in its surface and a female die adapted to receive the male die, the hob is pressed into the sheet metal to shape the sheet metal, and the shaped sheet metal is set in a hemispherical recess in a mold base. Alternatively, a mold base of relatively mild metal having a recess is furnished and the hemispherical master male die or hob is directly pressed against the recess of the mold base for shaping the mold.
In the precision casting technique, silicone rubber is applied to the surface of the master male die, followed by vulcanization to form a female die. The female die is filled with a ceramic material to form a ceramic male die. Thereafter, a frame is formed around the ceramic male die from a ceramic material such that the ceramic male die is located inside the frame and a cavity corresponding to the outside configuration of a desired mold is defined in the frame. Molten metal is cast into the cavity through a gate on the frame and cooled therein. Removal of the surrounding ceramic portions including the male die and frame leaves the mold.
The electric discharge machining technique involves placing a male die close to a female die having a ball-shaped recess with a smooth surface, and generating an electric discharge therebetween, thereby forming dimple-forming projections on the recess surface of the female die.
In the electroforming technique, a thick plating layer, for example, using nickel is formed on the surface of a male die by a plating process. The plating layer is removed from the male die and used as a patterning portion of a mold.
The hobbing technique is advantageous in cost, but is limited in the precision of the ball molding surface because the molding surface is formed of a thin sheet metal or relatively mild metal. Durability is poorest among the aforementioned techniques. Precision cast molds are improved in molding precision and durability, but expensive due to the complication of the process. The molds formed by electric discharge machining are highly durable, but low in molding precision. The cost is high because a master male die must be furnished for every mold. Electroformed molds are improved in molding precision and durability, but cannot avoid an increased cost because a master male die must be furnished for every mold as in the case of electric discharge machining.
As described above, the traditional methods for preparing golf ball molds have advantages and disadvantages. There is a desire to have a method for preparing a mold which is improved in all of molding precision, durability and cost.